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` FFaZanaerobic derlying sandy silt strata in the exploratory boring. Rust mottling occurs when cteria decompose organic matter and use iron(Fe") in their metabolic processes. n of iron creates rust. When these two conditions are present - organic matter and �. environment - denitrification (the conversion of nitrate to gaseous products and thee by which nitrate concentrations are reduced) is promoted. Although mottling may be attributed to geologic processes, it is most probably due to seasonal soil saturation whereby percolating soil water encounters slower permeability strata and accumulates on top of this strata. Soil samples were obtained from two areas in proposed leachfield areas for chemical analyses. The first sample was composited from subsamples obtained from 40 inches below grade in Parcels 1 through 7. As the noted on the SOIL ANALYSIS REPORT under SAMPLE NUMBER PL1-7,the nitrate-nitrogen(NO3-N) concentration is a very low 2 ppm. For ` comparison purposes,the second sample was obtained from the vineyard in Parcel 8, and is referenced under SAMPLE NUMBER as GRPS. The nitrate-nitrogen concentration is also very low at 4 ppm. Soil chemistry was done on the samples to analyze several constituents. The important parameters for nitrate loading assessment are the organic matter, pH, cation exchange capacity (CEC), clay content percentage, soluble salts, along with nitrate-nitrogen content. As noted,the soluble salts are low at 0.3 mmhos/cm. Organic matter in the soil is also low at 0.8%, with an estimated nitrogen release (ENR) of 46 lbs NO3-N per acre. This indicates a very low potential for future nitrate-nitrogen loading. Since septic effluent is composed predominately of ammonium(NH4) ions,the pH, along with the CEC, are significant influences on ammonium molecules. The pH of the soil is neutral-to-somewhat alkaline which may slightly inhibit ammonium formation and stability, and may create a small propensity for ammonia(NH3) formation. The CEC measures the ability of the soil to theoretically trap and hold ammonium molecules. The loamy sand soil with a CEC of 4.8 and 7.2 suggests there is very little potential for the ` retention of ammonium molecules for microbial uptake and suppression of nitrification(nitrate formation). The CEC probably decreases with lower soil profile depth. Clay soils have a higher CEC than other soil types. Cations(positively charged ions) such as NH4', K', Ca"and Mg" are removed from solution by the clay soil fraction because the clay particles possess a negative charge. In cation exchange, a positively charged ion within the clay complex is ., replaced and released by another type of ion. Ionic exchange, through its effects on nutrient availability and acidity, has a tremendous effect on biological and chemical transformations. The significance of cation exchange becomes important when the chemistry of septic effluent is analyzed. Nitrogen in septic tank effluent consists of approximately 75%N in the ammonium ion (NH4') form and 25%N in the organic form. If the ammonium ion is bound and eventually utilized,nitrification cannot occur. Nitrification is an aerobic reaction accomplished predominately by autotrophic bacteria which convert ammonium (NH4')to nitrite (NOD and subsequently to nitrate(NO3). 3 'valley Ag Research